1. Technical Field
The present invention relates to a current sensor which detects the current of each phase of three-phase alternating current and is, in particular, characterized by the structure of a shield.
2. Background Art
A current sensor has been known which detects the current flowing through a current path (for example, a bus bar, etc.) for connecting an in-vehicle battery of a vehicle and electrical equipment of a vehicle to each other. An example of such a current sensor is illustrated in FIG. 8 (see JP-A-2010-223868).
FIGS. 8A and 8B show a current sensor 100 according to a related art, FIG. 8A is an exploded perspective view thereof and FIG. 8B is a longitudinal sectional view of essential parts thereof. The current sensor 100 includes a housing 200 and a shield 500 fixed to the housing 200. Further, the current sensor 100 includes a current path 600 arranged between the housing 200 and the shield 500 to detect the current flowing through the current path 600. The current is measured by detecting the magnetic strength using a magnetic detection element 400 mounted on a substrate 300 attached to the housing 200 and outputting electric power corresponding to the magnetic strength. The shield 500 has a substantially U shape and completely surrounds the back side of the current path 600 (see FIG. 8B). With this configuration, it is possible to realize the current sensor 100 in which magnetic distortion do not occur and reliability is high. Although not disclosed in JP-A-2010-223868, FIG. 8B is prepared for clarifying the difference between the configuration of the present invention and the related art.
In the current sensor 100 disclosed in JP-A-2010-223868, particularly, the shield 500 completely covers the current path 600 from the back side thereof in the attachment portion of the current sensor 100. For this reason, there is a disadvantage that the eddy current is generated by the current flowing through the current path 600 and the phase of the magnetic field detected by the magnetic detection element 400 is delayed as compared to the phase of the current. Accordingly, there is a problem that reliability in a high-speed responsiveness is lowered. Further, in the large current of high frequency, magnetic saturation of the shield is expected and a linear relationship between the current and the magnetic flux density detected by the magnetic detection element 400 is broken. As a result, measurement within an allowable error range is difficult. Further, in the current sensor 100 according to the related art, it is possible to obtain a good response characteristic in the current detection of three-phase alternating current having a low peak value by shifting the position of the magnetic detection element to the left and right from the center of the current sensor. However, in this case, there is also a problem that the magnetic interference from the adjacent phase current path occurs.
Accordingly, the present invention has been made to solve the above-described problems and an object of the present invention is to provide a current sensor in which a high-speed responsiveness for detecting the magnetic field generated by the current flowing through the current paths of three-phase AC becomes good and therefore the reliability is high.